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Author Topic: Smudge proposed NMR experiment replication.  (Read 126941 times)
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Re: Smudge proposed NMR experiment replication. « Reply #800 on: 2021-02-14, 21:25:32 »
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Hi Itsu,

It is okay that you can order the FT cores but I cannot tell how the lack of using such CMCs in this setup may influence the real goal of these tests.

You can use the FT-3K50TS and if they do not have too low permeabilty, then they could probably make better CMCs than the ferrite material manifested so far. Just try to wind 10 turns on them and measure inductance.
These cores are for CMCs....   see here: https://www.hitachi-metals.co.jp/e/product/finemet/cmc/core/ft-3k50t_f.html   

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #801 on: 2021-02-14, 21:33:55 »

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OK,  i have:

FT-3K50T F3020CS      18uH@100kHz Nano    and
FT-3K50T F6045GS      24uH@100kHz Nano


Will start with 10 turn coils.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #802 on: 2021-02-14, 21:42:26 »
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Perhaps the bigger one can accomodate 30-40 turns on any one of its half core area.  30 turns would give about 21.6 uH, 40 turns would give about 38.4 uH. 
   
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Re: Smudge proposed NMR experiment replication. « Reply #803 on: 2021-02-15, 09:25:55 »

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Hmmm,   one of the smaller ones had some windings on it, 7 turns and 12 turns and they measure 1mH and 3.5mH @100KHz (1mm od wire).

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #804 on: 2021-02-15, 14:45:18 »
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Well, it means that the correct data sheet for the core type is not found yet.   Your measurements show that this core must have very high permeability. 
From its OD, ID anf height data the permeability can be calculated if needed.

First you wrote FT-3K50TS for its type and I then gave link to FT-3K50T F series by mistake, and there was no data for FT-3K50TS.  I think this is the Finemet type which was finished by Hitachi years ago and this was a topic already somewhere here.
I suggest to make two windings with identical number of turns on it and check how it behaves in the setup.

EDIT:  from your L meter display in the upper right corner the Q quality factor is 1.27 at the 100 kHz test frequency.  This low Q may or may not forecast a bad behaviour for the core at 4 MHz, we shall see. 

Thanks, Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #805 on: 2021-02-15, 15:14:01 »

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Thanks Gyula,

the below attached data sheet shows a permeability of about 2000 at 4MHz, see Fig.2

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #806 on: 2021-02-15, 15:46:07 »
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Okay Itsu, that is fine.  Now it remains to be seen how it really behaves.   You will have some difficulty to trim the turns to get a reasonably close inductance value between the two windings.
   
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Re: Smudge proposed NMR experiment replication. « Reply #807 on: 2021-02-15, 20:22:20 »

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I put up 2 windings of 8 turns each on my finemet core, see picture.
They measure 979uH @ 100KHz each with the other coil open.
In series it measures 5.22uH @ 100KHz.

Without any cmc in the circuits and resonance tuned to 4MHz i have the white trace (94V).
With the finemet cmc in the output circuit and again tuned to resonance at 4MHz i have the purple trace (110V).

Sweeping from 3.5 to 4.5MHz.

 
Itsu 
   
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Re: Smudge proposed NMR experiment replication. « Reply #808 on: 2021-02-15, 20:40:25 »
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Itsu,  that is great news.  O0

Perhaps you could use the other Finemet core as a CMC at the output of the PA to drive the input of the pancake coils.  (Or put this CMC to the front to see any behaviour. )

Thanks,
Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #809 on: 2021-02-15, 21:01:30 »

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Hi Gyula,

how is it great news as WITH cmc the output signal gets stronger?

I understood from verpies his Post #739, see quote below, that a cmc would attenuate (unwanted) signals, so i would expect to see less (only the wanted) signal with a cmc installed.

Quote
The common mode interference signal, which can be picked up by an Earth-grounded scope, can be attenuated with multiple ferrite beads (or toroidal RF cores) which encompass BOTH wires connecting the toroidal coil.  These beads significantly increase the inductance of these wires, so they present a high inductive reactance path to the common mode signals. ...and because these beads encompass BOTH wires - they do NOT attenuate the differential signals.

Where do i go wrong?

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #810 on: 2021-02-15, 21:26:02 »
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Perhaps try to ask this question from yourself: why is it that the scope shows less output voltage without the CMC?   C.C

Very likely an asymmetrical measurement setup (i.e. without a CMC or CMCs in this case) uses up power what the CMC can confine and route to the load. 
Very likely, with no CMC,  some of the output signal can leak to the enviroment via the ground of the instrumentation, this may also mean we do not always get full output in certain setups, this much depends on the particular measurement circumstances.
This is my take on this.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #811 on: 2021-02-15, 21:39:14 »

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Gyula, 


ok,  i will ponder on that question some more later  :-\

For now i have added a 2th finemet cmc in the input circuit (just before the pancake coils).
It has similar 8 turns as the 1st one, but measures 1714 and 1715uH @ 100KHz  :D

The below screenshot shows the output when tuned again to 4MHz resonance with both finemet cmc's installed (48.6V).

Sweep again from 3.5 to 4.5MHz in 20s  (no heating up of the input cmc now).

Itsu

 
   
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Re: Smudge proposed NMR experiment replication. « Reply #812 on: 2021-02-15, 21:52:49 »
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Okay Itsu, I can ask these:

Has the SWR changed when you connected the 2nd CMC to the front of the pancake coils?

I assume you had to retune the trimmer capacitors after inserting the 2nd CMC?

What is the output when you replace the two CMCs with each other?

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #813 on: 2021-02-15, 22:12:14 »
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Quote from: Itsu on 2021-02-15, 21:39:14
...

ok,  i will ponder on that question some more later  :-\

...

I meant it would be also a valid question, sorry. 

Addition to my previous post:

Would you test the 2nd CMC at the output too?  (without using the 1st CMC)

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #814 on: 2021-02-16, 08:53:10 »

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Hi Gyula,

I did not check on the SWR lately, but will do that later today.

I always retune both sides trimmer caps when changing anything just to check i am on resonance in both circuits, so i assume it was needed here to, but not sure.

I will swap over the CMC's and check the 2nd CMC at the output without using the 1st CMC also later today.

Regards Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #815 on: 2021-02-16, 15:41:37 »

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Quote
Has the SWR changed when you connected the 2nd CMC to the front of the pancake coils?

Checking the SWR with the 2th finemet cmc on the input (and with 1st finemet cmc on output) shows about 1.5W going in at resonance and a low (1:1.3 or so) swr (not enough RF for full scale set).

Quote
What is the output when you replace the two CMCs with each other?

When swapping the 1st cmc with the 2th, the same output is seen (~50V), no retuning needed.


Note: yesterday i measured the 2th finemet cmc (8 turns each) to be 1714uH, but it also showed a value of 1.096uH each sometimes.
I never found out why these different values were shown, but it settled finaly to the strange high 1714uH value.
Today i meaured both cmc's again and the 2th now measures a steady 1096uH for each.
The 1st cmc now shows a steady 978uH each, so no change there.
I must assume that with both cmc's having the same amount of turns ( 8 ) their inductances should be very close, so the now measured 978 and 1096 are probably the real ones.
Not sure still why i measured the 1714 most of the times for the 2th cmc yesterday.


Quote
Would you test the 2nd CMC at the output too?  (without using the 1st CMC)

Removing the 1st cmc from the input, now only the 2th cmc on the output, needed to retune.
We have 126V now with the 2th cmc on the output (was 113V with 1st cmc there), SWR about 1:1 with 4W in on resonance see screenshot.

Swapping back to the 1st cmc again on the output and retuning (no cmc on input) we again have 114V with swr 1:1 at 4W.

So the 2th cmc with the slightly higher inductance (1096 v 978uH) gives higher output.

Itsu

« Last Edit: 2021-02-16, 20:06:07 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #816 on: 2021-02-16, 17:17:19 »

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Quote from: gyula on 2021-02-15, 21:26:02
Perhaps try to ask this question from yourself: why is it that the scope shows less output voltage without the CMC?   C.C

Very likely an asymmetrical measurement setup (i.e. without a CMC or CMCs in this case) uses up power what the CMC can confine and route to the load. 
Very likely, with no CMC,  some of the output signal can leak to the enviroment via the ground of the instrumentation, this may also mean we do not always get full output in certain setups, this much depends on the particular measurement circumstances.
This is my take on this.

Gyula

OK,  concerning your question above,  so you mean a groundloop problem.

I know i have my grounded FG as source and use my grounded scope on the output, so i changed to the differential probe measurement method for measuring the output.
Yellow and blue probe on each side of the 690K resistor, and the math function calculating blue - yellow, see screenshot.

The same output as 1 post / screenshot earlier (126V) now shows 205V!

Guess i have to revisite all my measurements done up till now using the differential probe method.


Itsu
« Last Edit: 2021-02-16, 20:06:27 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #817 on: 2021-02-16, 18:58:36 »
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Hi Itsu,

First on you last but one reply, my answer:
It looks like when there is a CMC at the input of the pancake coils, then SWR is around 1:1.3 and without it the SWR improves. You mention about 1.5 W going in with the 2nd CMC at the input: the CMC seems to influence input matching unfavorably. And then you find 5 W input without any CMC at the input (all these shown by the power and SWR meter, right?  you do not have a current probe). 

This may also mean the lower input power (whatever causes it to be lower) is to blame to have the smaller voltage of 50 Vpp or so at the output. 

Regarding your Note: As far as I know, these types of Finemet cores are not made of solid core material but of very thin Finemet laminated pieces of layers on top of each other to make up for the h size (height). And these laminations are put into a plastic case holder to give them a certain rigidness. I think it is possible that when you handle this core, the laminations inside may change their position a little and due to the high permeability, the effect may manifest as you experienced.  Perhaps measure this core again with the L meter and try to squeeze the core gently across its height by your fingers. Or try to flex the body of the core also very gently to see any change in the L value. This core has the higher OD versus the 1st CMC, right? so it may be more vulnerable to such small deformations. The rigidness of the plastic case also counts.

On you latest post above:
  It is okay that you revisit some measurements but perhaps try to start with checking for instance, with the usual single voltage probe,  the output open voltage of your FG set to a known value and then terminate it by 50 Ohm dummy load and check again etc.
Then the power amp may come because it brings in another 'ground' from the DC power supply and so on. 

Question: did you find the 205 Vpp with or without any CMC ?    :D

Thanks,
Gyula
   
img  Itsu
Re: Smudge proposed NMR experiment replication. « Reply #818 on: 2021-02-16, 20:38:54 »

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Quote
First on you last but one reply, my answer:
It looks like when there is a CMC at the input of the pancake coils, then SWR is around 1:1.3 and without it the SWR improves. You mention about 1.5 W going in with the 2nd CMC at the input: the CMC seems to influence input matching unfavorably. And then you find 5 W input without any CMC at the input (all these shown by the power and SWR meter, right?  you do not have a current probe). 

Yes, i agree, and yes all these shown by the power and SWR meter (so not very reliable), no current probe right now.

 
Quote
This may also mean the lower input power (whatever causes it to be lower) is to blame to have the smaller voltage of 50 Vpp or so at the output. 

Right, the lower the input, the lower the output.

Quote
Regarding your Note: ..........                       This core has the higher OD versus the 1st CMC, right?

It seems there is something going on inside this toroid, but i cannot invoke it by squeezing or knocking, its just there, then its not, and it needs the LCR meter to disconnect then reconnect to show up.

This core has the same OD as the first one, the two are identical.
I do have 2 other bigger OD Finemet cores, but did not use then yet.


Quote
On you latest post above:
It is okay that you revisit some measurements but perhaps try to start with checking for instance, with the usual single voltage probe,  the output open voltage of your FG set to a known value and then terminate it by 50 Ohm dummy load and check again etc.
Then the power amp may come because it brings in another 'ground' from the DC power supply and so on. 

The PA is fed from a PS with floating return line, so not grounded.

Quote
Question: did you find the 205 Vpp with or without any CMC ?

The 205V was found with the same situation as when i found the 126V, meaning with the 2th CMC on the output.
So i just switched from a single probe setup (ground lead) to a differential probe setup (no ground).

See the below diagram on the groundloop situation when using a single (grounded) probe.


I tried using a battery operated FG, but the PA did not like this floating input as it started to oscillate.



Itsu
« Last Edit: 2021-02-16, 21:27:25 by Itsu »
   
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Re: Smudge proposed NMR experiment replication. « Reply #819 on: 2021-02-16, 23:33:20 »

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Quote from: gyula on 2021-02-14, 21:25:32
It is okay that you can order the FT cores but I cannot tell how the lack of using such CMCs in this setup may influence the real goal of these tests.
Quote from: Itsu on 2021-02-15, 21:01:30
I understood from verpies his Post #739, see quote below, that a cmc would attenuate (unwanted) signals, so i would expect to see less (only the wanted) signal with a cmc installed.
Where do i go wrong?
The ideal goal without water is to obtain 0V amplitude at the output (the toroidal coil) when a source of the signal is applied to the input (pancake coils). Of course that ideal can only be approached.
Part of the signal appearing at the output comes from the common-mode admittance between the input an output. The role of the CMCs is to attenuate that as much as possible, leaving the unobstructed path only for differential signals.

When the E- shielding is done correctly, the S21 series measurement between points A and B should be very low, indicating that no common mode signal is getting through the inter-winding capacitances (CIW) and ambient (CAMB). 
By shorting the terminals of the coils during this measurement it is assured that no current flows in the coil windings and no magnetic flux is generated/received by the coils and all energy between the input and output is transferred through the stray capacitances and the E-field, which should be effectively shunted to the RF ground by the E-shield ...and CMCs (or beads)  should further attenuate whatever remains.  Do they?
« Last Edit: 2021-02-17, 00:59:30 by verpies »
   
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Re: Smudge proposed NMR experiment replication. « Reply #820 on: 2021-02-17, 00:45:55 »

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Quote from: gyula on 2021-02-16, 18:58:36
It looks like when there is a CMC at the input of the pancake coils, then SWR is around 1:1.3 and without it the SWR improves.
We have to be very careful when using the phrases "SWR improves" or "better SWR" in reference to this system, because this is not an RF transmitter!
Ideally, the SWR between the PA and the "tuner should be 1:1, and the SWR between the "tuner" and the Pancake coils should be 1:∞.
...and the voltage amplitude between the toroidal coil's terminals should be 0V without water.

Of course this "ideal" can only be approached.
   
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Re: Smudge proposed NMR experiment replication. « Reply #821 on: 2021-02-17, 09:32:26 »

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Verpies,

thanks, i will setup this "S21 series measurement" without any water to get a base line and add the cmc's to see any difference.

Itsu
   
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Re: Smudge proposed NMR experiment replication. « Reply #822 on: 2021-02-17, 10:22:30 »
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Itsu, thanks for your answers and all your efforts.

Verpies,  okay and thanks for the additional explanations.

Gyula
   
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Re: Smudge proposed NMR experiment replication. « Reply #823 on: 2021-02-17, 13:09:03 »

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@Gyula, Smudge

You are welcome to improve on my diagram in "Cap coupling2.png" to show other modes of energy transfer in this system.  Perhaps you can envision other paths through which this energy can be transferred from input to output by non-H fields.
The E-field transfer through the CAMB and the free floating conductor at the top of my diagram does not have to be the only one.
   
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Re: Smudge proposed NMR experiment replication. « Reply #824 on: 2021-02-17, 15:16:35 »

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A first "S21 series measurement" using as "plane of reference" the points A and B in the diagram (A = port 1, B = port 2 of the nanoVNA).

So no CMC's, (input) tuner or output circuit used.

First screenshot is with the toriod shield floating (not connected)
Second screenshot is with toroid shield connected to nanoVNA outer connectors.

Itsu
« Last Edit: 2021-02-17, 15:44:49 by Itsu »
   
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